Fail-safe dry friction clutch for a vehicle accessory

ABSTRACT

A fail-safe friction clutch assembly for a vehicle accessory, particularly to drive a vehicle cooling pump, and more particularly as part of a dual mode drive for a cooling pump, together with an electric motor. The friction clutch assembly includes a friction plate member connected to a central rotatable shaft member used for operating the vehicle accessory. A pair of friction lining members are positioned on opposite sides of the friction plate member. An armature member is spring biased to axially force the friction plate member and friction lining member against a housing or cover which is rotating at input speed. A solenoid assembly is used to overcome the spring bias and pull the armature and friction plate member away from the housing.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser. No. 61/745,647 filed on Dec. 24, 2012.

TECHNICAL FIELD

Friction clutch assemblies, particularly for vehicle accessories, such as hybrid coolant pumps, are disclosed.

BACKGROUND

Water pumps are used in water cooled engines, primarily for operation of vehicles such as automobiles and trucks with internal combustion engines. The water pumps are typically driven by a belt attached to the crankshaft of the engine and thus operate at some percentage of engine speed. The pumps have an impeller that is used to circulate the engine coolant from the engine to the radiator and back in order to keep the coolant within acceptable temperature limits.

Efforts are being made today to reduce the power consumption of engine accessories, such as water pumps, in order to improve fuel economy and reduce emissions. It would thus be preferable if such accessories, including water pumps, could be made to operate at variable speeds or with less power in order to reduce the load on the engine and, in turn, improve fuel economy and reduce undesirable emissions from the engine.

SUMMARY OF THE INVENTION

A vehicle accessory having an improved dry friction clutch mechanism is disclosed. In one form, the present teachings provide a friction clutch assembly that includes a solenoid assembly, an armature, a rotary housing, a friction plate, a return spring, and a plurality of biasing members. The solenoid assembly is configured to produce a magnetic field. The armature is configured to move along an axis in response to application of the magnetic field generated by the solenoid assembly. The armature is movable between a first armature position and a second armature position. The rotary housing is coupled to the armature for rotation about the axis. The friction plate is movable along the axis between a first friction plate position and a second friction plate position. The return spring biases the friction plate along the axis toward the first friction plate position. The biasing members bias the armature along the axis toward the second armature position. When the armature is in the first armature position, the friction plate is coupled for rotation with the armature and the rotary housing. When the armature is in the second armature position, the friction plate is not coupled for rotation with the armature or the rotary housing.

Further objects, features and benefits of the invention are set forth below in the following description of the invention when viewed in combination with the drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a vehicle water pump assembly which can incorporate the present invention.

FIG. 2 is a cross-sectional view of the assembly shown in FIG. 1 and featuring an embodiment of the present invention.

FIGS. 3A and 3B are exploded views of the components of the assembly as shown in FIG. 2.

FIG. 4 is an enlarged cross-sectional view of the assembly shown in FIGS. 2-3 with the components shown in the solenoid disengaged position.

FIG. 5 is an enlarged cross-sectional view of the assembly shown in FIGS. 2-3 with the components shown in the solenoid engaged position.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

For the purpose of promoting and understanding the principles of the present invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe them. It will nevertheless be understood that no limitation as to the scope of the invention is hereby intended. The invention includes any alternatives and other modifications in the illustrated devices and described methods and further applications of the principles of the invention which would normally occur to persons or ordinary skill in the art to which the invention relates.

The present inventions described herein relate to friction clutch assemblies particularly used for coolant pumps which circulate the coolant in an engine, such as an automobile internal combustion engine. (The terms “water pump” and “coolant pump” are used interchangeably herein.) The present invention, however, can also be used for other engine accessory devices.

The preferred embodiment of the present invention as described herein is particularly adapted for use with trucks, passenger cars and off-highway vehicles, and will be described with respect to its use in a dual mode coolant pump. In accordance with a preferred embodiment, the electric motor is a brushless DC (BLDC) motor. For the mechanical mode of operation, the water pump is driven by an engine belt, such as a serpentine accessory belt, attached to the crankshaft of the engine.

As a dual mode coolant pump, the pump is electrically driven under most conditions. However, it also can be mechanically engaged where more cooling is required. Thus, when the vehicle is being driven under most normal conditions, the water pump is being driven and operated by the electric motor.

During “worst case” cooling conditions, such as when the vehicle is heavily loaded, when it is pulling a trailer, or when it is going up hill in the summertime, etc., the water pump is adapted to be mechanically driven by the belt directly from the engine. This provides the necessary cooling under such circumstances. In some circumstances, it may be necessary or possible to perform both modes of operation.

A hybrid (dual mode) water pump embodiment with a friction clutch assembly in accordance with the present invention is shown in FIGS. 1-5 and referred to generally by the reference numeral 20. The hybrid water pump includes a motor housing 22, a solenoid housing 24, a pulley member 26 and a cover member 28. A central shaft member 30 is rotated by the pump 20 which operates the water pump impeller 32. As shown, the pulley member has a smooth outer surface 27 on which an engine belt (not shown) is positioned. The outer surface of the pulley member could also comprise circumferential grooves for mating with an engine belt with corresponding grooves.

A cross-sectional view of the water pump assembly 20 is shown in FIG. 2 and an exploded view of the components of the water pump assembly 20 is shown in FIG. 3. Enlarged views showing the friction clutch mechanism in the deactivated and activated modes of operation are shown in FIGS. 4 and 5.

The water pump assembly has an impeller shaft 30 which is positioned within the assembly and is attached to a water pump impeller 32. The impeller shaft 30 is held in place in the multi-component assembly by bearings 34 and 36. A coolant seal 38 is used to prevent coolant in the pump from leaking into the motor housing.

A motor 50 is positioned inside the motor housing 22. The motor 50 includes a rotor carrier 52, magnets 53, and a stator 54. Magnets 53 are bonded to the rotor carrier 52 and together form the rotor of the motor. The motor 50 is preferably a brushless DC (BLDC) electric motor. The rotor 52 is securely attached, e.g. press fitted, to the shaft 30, which causes the shaft, and thus the impeller 32, to rotate when the motor 50 is operated. Electricity to the motor 50 is supplied by an electrical source (not shown).

The motor housing 22 has a plurality of mounts, only two of which 23, 25, are shown in the drawings. The mounts have openings for attachment of the water pump assembly 20 inside the engine compartment of a vehicle.

The friction clutch assembly is designated generally by the reference numeral 60. The friction clutch assembly generally comprises an armature plate 62, a friction plate 64, and two annular rings of friction material 66 and 68. The armature plate 62 is preferably made of a magnetic metal material, such as low carbon steel. The friction plate 64 is preferably made of a non-magnetic material, such as stainless steel. The friction material 66 and 68 can be any conventional friction materials used in friction clutches today, and can be complete rings, segments of rings, or simply pieces of friction material positioned generally where rings 66 and 68 are positioned in the drawings. Preferably, the friction materials 66, 68 are bonded to the friction plate 64 using a bonding agent.

The cover member 28 which preferably is made of a non-magnetic material, such as stainless steel, is connected directly to the pulley member 26 by a plurality of connecting pin members, such as fasteners or bolts 72. The ends of the fasteners can be threaded (as shown particularly in FIG. 2) for mating with corresponding mating threads in openings 74 in the pulley member 26. Thus, when the pulley is rotated by an engine belt (not shown); the cover member 28 rotates at the same input speed.

The pulley member 26 is preferably made of a magnetic metal material, such as low carbon steel. The pulley member rotates freely around bearings 80. Although the bearings can be of any type that will have sufficient durability and performance, a pair of stacked bearings can be utilized, as shown in the drawings.

The operation of the friction clutch assembly is performed by a solenoid assembly 90. The solenoid assembly includes a solenoid coil 92 which is positioned in the solenoid housing 24. The solenoid coil member comprises a donut-shaped coil of copper wires, while the solenoid housing is preferably made of a magnetic material, such as low carbon steel. The solenoid coil member 92 is potted in the solenoid housing 24.

The solenoid housing 24 is independently positioned in the water pump assembly by use of bearing 36. The bearing 36 allows the shaft member 30 to rotate freely relative to the solenoid housing 24.

The solenoid housing 24 is connected directly to the motor housing 22 by, for example, a press fit and/or a series of fastener members 29. In production, several different ways can be used to anchor or fix the solenoid housing 24 to the motor housing 22.

The nut member 102 is threaded, or otherwise thinly fixed, on the end of the shaft member 30. The friction plate member 64 is connected, such as being keyed, to the nut member 102. As shown in FIG. 3A, the nut member has a plurality of spline members 103 which fit within corresponding notches 65 in the center of the friction plate member 64. In this manner, the nut and friction plate members rotate with the shaft member 30. The nut member 102 and the shaft member 30 firmly clamp the stop member 100 and the bearing member 36 together. The shaft member 30 and all components fixed on it are positioned axially by the bearing member 36. The stop member 100 is preferably made of a non-magnetic material, such as stainless steel.

To fix the bearing member 36 in an axial position inside the solenoid housing 24, a wave spring member 104 and bearing retainer member 106 are utilized. The bearing retainer member 106 is threadedly affixed to the solenoid housing as shown by reference number 101 (see FIG. 4).

The stop member 100 is utilized to stop the axial movement of the friction plate member 64 when the solenoid assembly 90 is energized, as explained below. A return spring 110 is positioned between the nut member 102 and the friction plate member 64 and acts to return the friction plate member 64 to its mechanical disengaged position when the solenoid assembly 90 is actuated.

As indicated, the water pump impeller 32 is normally driven by the electric motor 50. The electric motor and the solenoid coil are electrically powered through a circuit board (not shown). Electrical leads and wires can be insert molded in the motor housing 22 in order to carry the electrical signals to the electric motor 50 and solenoid coil member 92. The circuit board further communicates with the electronic control unit (ECU) of the vehicle through the vehicle communication network such as a CAN network. The water pump assembly controller circuit board could also be positioned inside the motor housing 22 possibly having a donut shape.

The speed of the motor and thus the water pump is selected according to the cooling required for the engine. Sensors feed relevant data to the ECU which then sends a signal to the pump controller requesting the desired speed. The pump controller then determines whether the desired speed is best achieved using the electric motor or by engaging the friction clutch and driving the impeller directly from the pulley.

When the water pump is being driven solely by the electric motor 50, the friction clutch assembly is held in a disengaged position by the solenoid assembly 90. This is shown in FIG. 5. When the solenoid coil member 92 is electrically activated, a flux circuit 120 is created which acts to pull the armature plate 62 toward the solenoid coil member overcoming the force of the coil spring members 108. With the armature plate 62 pulled toward the solenoid, the return spring 110 holds the friction plate 64 against the stop member 100. In this condition, the friction materials on the friction plate 64 are not in contact with either the cover member 28 or the armature plate 62.

The number of coil springs 108 and their biasing force is determined according to the force needed in the assembly. Six coil springs 108 are shown in the drawings, but there can be more or less than this amount depending on the force needed.

In this electrical mode of operation, there are air gaps on both sides of the friction materials on the friction plate, and the input (pulley member) and output (shaft member) are completely disconnected. This eliminates any interaction, such as bearing drag between the input and output.

In order to create an appropriate flux circuit 120, the pulley member 26 has a plurality of openings 115 which create air gaps. The openings 115 essentially form an annular open ring. With the air gaps, the pulley member is for electromagnetic purposes, essentially an outer annular ring 116 and a separated annular inner ring 118. (This is best shown in FIG. 3B.)

The flux circuit 120 is shown in FIG. 5. It runs through the solenoid housing 24, the belt engaging portion of the pulley member 26, outer annular ring portion of the pulley member 26, and then jumps to the armature plate member 62 and then back to the inner annular ring portion of the pulley member 26 where it returns to the solenoid housing. This circuit pulls the armature member tightly to the pulley member such that the armature member rotates with the pulley member and at the same speed.

FIG. 4 depicts the situation where the solenoid assembly 90 is not activated. This causes the water pump to be driven mechanically by an engine belt and the electric motor 50 can be turned off. In this situation, coil springs 108 force the armature member 62 in a direction away from the pulley member and away from the solenoid assembly. This causes the armature member 62 to contact the friction member 68 which in turn forces the friction member 66 to contact the inner surface 28A of the cover member 28. Since the armature member, pulley member and cover member are all fixed together, this causes the shaft member 30 to rotate at the same speed.

A path of torque transfer which mechanically rotates the shaft member is shown by arrows 130 in FIG. 4. In the engaged clutch, the friction plate member is clamped between the cover member and armature member and torque is transferred through both sides of the friction plate. There also is a torque transfer path from the pulley member 26, through the fastener 72, the armature plate member 62, the friction plate member 64, the nut member 100 and to the shaft 30.

It is common in automotive accessories such as air conditioning compressors, pumps, etc. to use spring engaged, electromagnetically disengaged clutches to selectively turn on and off the drive to the accessory component. This is typically done to conserve energy when the device is not needed. These devices are typically designed to be spring engaged so the accessory device is powered in the event of a control failure such as a loss of electrical power. This is done to provide “Fail-Safe” functionality meaning that the device defaults to its “on” state when it is unpowered.

As indicated above, the present invention provides a “fail-safe” friction clutch design. If the electrical system of the coolant pump were to fail, the solenoid would be de-energized allowing the coil springs to force the friction clutch assembly to become engaged. Therefore the pump would operate in mechanical mode with the impeller driven by the pulley member through the clutch assembly, thus preventing overheating.

Although the invention has been described with respect to preferred embodiments, it is to be also understood that it is not to be so limited since changes and modifications can be made therein which are within the full scope of this invention as detailed by the following claims. 

What is claimed is:
 1. A friction clutch assembly for a vehicle engine accessory, said friction clutch assembly comprising: a solenoid assembly that is configured to produce a magnetic field; an armature that is configured to move along an axis in response to application of the magnetic field generated by the solenoid assembly, the armature being movable between a first armature position and a second armature position; a rotary housing that is coupled to the armature for rotation about the axis; a friction plate that is movable along said axis between a first friction plate position and a second friction plate position; a return spring biasing said friction plate along said axis toward said first friction plate position; and a plurality of biasing members biasing said armature along said axis toward said second armature position; wherein when said armature is in said first armature position, said friction plate is coupled for rotation with said armature and said rotary housing and wherein when said armature is in said second armature position, said friction plate is not coupled for rotation with said armature or said rotary housing.
 2. The friction clutch assembly of claim 1, wherein said biasing members comprise coil springs.
 3. The friction clutch assembly of claim 1, further comprising a first friction lining member disposed between said friction plate and one of said housing member and said armature.
 4. The friction clutch assembly of claim 1, further comprising a second friction lining member disposed between said friction plate and the other one of said rotary housing and said armature.
 5. The friction clutch assembly of claim 1, wherein said solenoid assembly comprises a solenoid housing and a solenoid coil that is received in the solenoid housing.
 6. The friction clutch assembly of claim 5, further comprising a shaft, wherein said friction plate is coupled to said shaft for common rotation and wherein a first bearing is received between said solenoid housing and said shaft, said first bearing supporting the shaft for rotation relative to said solenoid housing.
 7. The friction clutch assembly of claim 6, further comprising a second bearing, wherein said rotary housing comprises a pulley and a cover, wherein said armature and said friction plate are disposed along said axis between said pulley and said cover, and wherein said second bearing is disposed between said pulley and said solenoid housing and supports said pulley for rotation relative to said solenoid housing.
 8. The friction clutch assembly of claim 1, further comprising a shaft that is coupled to said friction plate for common rotation.
 9. The friction clutch assembly of claim 8, further comprising an electric motor, said electric motor having a rotor that is coupled to said shaft for common rotation.
 10. The friction clutch assembly of claim 9, further comprising a motor housing, wherein said solenoid assembly comprises a solenoid housing and a solenoid coil that is housed in said solenoid housing, wherein said electric motor is housed in said motor housing, and wherein said motor housing is coupled to said solenoid housing.
 11. The friction clutch assembly of claim 8, further comprising an impeller coupled to the shaft for rotation therewith.
 12. The friction clutch assembly of claim 8, further comprising an impeller coupled to the central shaft for rotation therewith.
 13. A friction clutch assembly for a vehicle accessory, said friction clutch assembly comprising: a solenoid assembly comprising a solenoid housing and a solenoid coil a pulley that is rotatable about an axis; a cover attached to said pulley and rotatable therewith; a central shaft that is rotatable about said axis; an armature that is movable along the axis between a first armature position and a second armature position; a plurality of biasing members biasing said armature along said axis toward said first armature position; a friction plate member coupled to said central shaft member for common rotation, said friction plate member being moveable along said axis relative to said shaft between a first friction plate position and a second friction plate position; a return spring biasing said friction plate toward said second friction plate position; a first friction lining member positioned on a first surface of said friction plate; and a second friction lining member positioned on a second surface of said friction plate said second surface being opposite said first surface; wherein said solenoid coil is selectively operable to cause said armature member to move from said first armature position to said second armature position, wherein when said armature is in said first armature position, said friction plate is coupled for rotation with said armature and said rotary housing and wherein when said armature is in said second armature position, said friction plate is not coupled for rotation with said armature or said rotary housing.
 14. The friction clutch assembly of claim 13, wherein said biasing members comprise coil springs.
 15. The friction clutch assembly of claim 13, wherein said first and second friction lining members each comprise annular rings of friction lining material.
 16. The friction clutch assembly of claim 13, wherein said pulley defines a plurality of circumferentially-extending slots that are disposed in-line with the solenoid coil.
 17. The friction clutch assembly of claim 13, wherein said pulley and said cover are attached together by a plurality fasteners.
 18. The friction clutch assembly of claim 17, wherein said fasteners are threaded fasteners.
 19. The friction clutch assembly of claim 13, further comprising a nut member that is threaded to said central shaft, wherein said friction plate is non-rotatably but axially slidably coupled to the nut member.
 20. The friction clutch assembly of claim 13, further comprising an electric motor, said electric motor having a rotor that is coupled to said central shaft for common rotation.
 21. The friction clutch assembly of claim 20, further comprising a motor housing, wherein said electric motor is housed in said motor housing, and wherein said motor housing is coupled to said solenoid housing.
 22. A dual mode drive device for a vehicle accessory comprising: a housing; a shaft in said housing and rotatable about an axis; an electric motor in said housing, said electric motor having a rotor that is coupled to the shaft for common rotation; and a friction clutch assembly comprising: a solenoid assembly with a solenoid coil; a pulley that is rotatable about the axis; a cover attached to said pulley and rotatable therewith; an armature member that is movable along the axis between a first armature position and a second armature position; spring members biasing said armature along said axis toward said first armature position; a friction plate connected to said shaft for rotation therewith, said friction plate being movable along said axis between a first friction plate position and a second friction plate position; a return spring biasing said friction plate toward said second friction plate position; a first friction lining member positioned on a first surface of said friction plate; and a second friction lining member positioned on a second surface of said friction plate, said second surface of said friction plate being opposite said first surface; wherein when said armature is in said first armature position, said friction plate is coupled for rotation with said armature and said rotary housing, and wherein the solenoid coil is selectively operable to generate a magnetic field that moves the armature out of the first armature position and toward the second armature position to thereby interrupt power transmission through the friction clutch assembly.
 23. The dual mode drive device of claim 22, wherein said electric motor is a brushless DC motor.
 24. The dual mode drive device of claim 22, further comprising an impeller coupled to the shaft for rotation therewith.
 25. The dual mode drive device of claim 22, wherein said spring members comprise a plurality of coil spring members.
 26. The dual mode drive device of claim 22, wherein said first and second friction lining members each comprise annular rings of friction lining material.
 27. The dual mode drive device of claim 22, wherein said pulley defines a plurality of circumferentially-extending slots that are disposed in-line with the solenoid coil.
 28. The dual mode drive device of claim 22, wherein said pulley and said cover are attached together by a plurality of fasteners.
 29. The dual mode drive device of claim 28, wherein said fasteners are threaded fasteners.
 30. The dual mode drive device of claim 22, further comprising a nut member that is threaded to said central shaft, wherein said friction plate is non-rotatably but axially slidably coupled to the nut member. 